The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
BSSID basic service set ID
CTRL control
DA destination address
E-UTRAN evolved UMTS terrestrial radio access network
FCC Federal Communications Commission
FCS frame check sequence
IBSS independent basic service set
ID identifier
IEEE Institute for Electrical and Electronics Engineers
ISM industrial, scientific and medical
LTE-A long term evolution (of E-UTRAN)-advanced
MAC medium access control
PHY physical
RAT radio access technology
RX receive
SA sender address
SSID service set identifier
TVBD television band device
TVWS television white spaces
TX transmit
WLAN wireless local area network
As radio spectrum for public use becomes increasingly burdened, research has turned recently to exploiting license-exempt radio spectrum such as the ISM band and what in the United States are known as TVWS. In general license-exempt radio spectrum is sometimes referred to as a shared band, contrasted with conventional cellular systems which utilize radio spectrum for which the system operator holds a license from a government regulator such as the FCC in the United States. There are various ways being considered to exploit this license-exempt spectrum, including direct device-to-device communications and offloading traffic from the cellular/licensed band onto the license-exempt band when the licensed band becomes too congested. Whether for traffic offload or otherwise, use of the license-exempt spectrum may in some cases be coordinated by the licensed spectrum radio systems, or in other cases they may be used by a stand-alone cell such as a LTE-A femto cell which provides fast access to the Internet in a similar manner to the WLAN specifications at IEEE 802.11.
TVWS is a particular portion of the license-exempt spectrum which was at one time set aside for television broadcast but which in recent years has become increasingly available for other uses. TVWS is suitable for radio communications due to their available large bandwidths at frequencies which are suitable for many different radio applications. But availability of the whole TVWS bandwidth is not complete, and so it is envisioned that there will be whitespace or TV band databases indicating for specific geographic areas or geo-locations which portions of that license-exempt spectrum are available to parties other than those involved with television broadcasting. Such portions may be identified in the relevant database as indexed channels, bandwidth and center frequency, upper and lower frequency bounds, or other frequency-definitive parameters. One of several reasons these envisioned databases need to be geographically specific is that television spectrum administration is not universal but is often country-specific. Another is that television broadcasts in one but not all regions of a country may need a portion of the spectrum for only a limited time.
Relevant to TVWS in the United States, the FCC defines two concepts for the help of find available channels; a TV bands database as summarized above and the geo-location capability. See for example document FCC 10-174; SECOND MEMORANDUM OPINION AND ORDER; UNLICENSED OPERATION IN THE TV BROADCAST BANDS—ADDITIONAL SPECTRUM FOR UNLICENSED DEVICES BELOW 900 MHz AND ABOVE 3 GHz BAND (adopted and released Sep. 23, 2010). The TV band database will maintain records of all authorized services in the TV frequency bands and so is capable of determining the available channels as a specific geographic location. Such available (or equivalently the used) channels are provided as lists to TVBSs that have been certified under the FCC's equipment authorization procedures. Some of the TVBDs will have a geo-location capability, and those devices should be able to determine their own geographic coordinates within a certain level of accuracy (+/−50 m). This capability is used with a TV bands database to determine the availability of TV channels at a TVBD's geo-location. The FCC defines several types of TVBDs as follows based on their characteristics.
A fixed TVBD is located at a specified fixed location and is able to: select a channel from the TV bands database; initiate and operate a network (by sending enabling signals to other fixed TVBDs or personal/portable TVBDs); and provide to a Mode I personal/portable device (see below) a list of available channels on which the Mode I device may operate (about TV channel 20) and a supplemental list of available channels for Mode I devices (these available channels are adjacent to occupied TV channels and are those on which a fixed TVBD cannot operate). Examples of what may operate as a fixed TVBD in the LTE system include an access node/eNodeB, a mobility management entity MME, a serving gateway S-GW, a local gateway L-GW, and a packet gateway P-GW. Similarly functioning nodes in other radio access networks may also serve the functions of a fixed TVBD. The maximum power a fixed TVBD is allowed to deliver to its TX antenna shall not exceed 1 W, and the maximum power spectral density (any 100 kHz during any time interval of continuous transmission) is 12.2 dBm.
A Mode I personal/portable device is another of the FCC's TVBD types. This type does not use any internal geo-location capability it may have (if any) to find its TVWS channels so even if it has access to a TV bands database the mode I device obtains a channel list from either a fixed TVBD or from a Mode II personal/portable TVBD (see below). A Mode I device may operate only as a client or dependent station/device, but not as an enabling station/device.
A Mode II personal/portable device is a portable device having similar functions as a fixed TVBD, but does not need to transmit/receive signals at a specified and fixed place. For personal/portable TVBDs, the maximum effective isotropic radiated power (EIRP) is 100 mW (20 dBm). If the personal/portable TVBD does not meet the adjacent channel separation requirements (the distance between the TVBD and the TV station is smaller than the minimum distance requirement), the maximum EIRP is set to 40 mW (16 dBm). The maximum power spectral densities for personal/portable devices operating adjacent to occupied TV channels is −1.6 dBm, otherwise 2.2 dBm.
And finally the FCC has designated a sensing only device, which is a personal/portable TVBD that uses spectrum sensing to determine a list of available channels. It can use the frequency bands 512-608 MHz (TV channels 21-36) and 614-698 MHz (TV channels 38-51). It is worthy to know that spectrum sensing is only defined for personal/portable TVBDs. The maximum power spectral density for sensing only devices is −0.8 dBm.
The IEEE 802.11af standard being drafted is intended to fulfill the above requirements in its TVWS operation. Relevant to this endeavor are the FCC's further requirements that Mode I devices are to be enabled by a Mode II device (called enabling station) as outlined in the document FCC 10-174 cited above. Once the mode I device is enabled it may start transmission on an available television channel or channels (more generally, a TVWS frequency resource).
Two or more Mode I TVBDs may form an IBSS network with one another, which is one type of an ad hoc network. An IBSS is a stand-alone basic service set that has no backbone infrastructure and which has two or more stations. Non-enabled Mode I TVBDs are not allowed to transmit before becoming enabled but they may listen to the transmissions of other devices. Mode I TVBDs become enabled by getting the relevant channel list from an enabling device, which may be a Mode II TVBD or a fixed TVBD. Once enabled, the Mode I TVBDs have to regularly receive an enabling signal from the Mode II or fixed TVBD which enabled its operation and provided the channel list. However, it is not clear yet exactly how the non-enabled Mode I device can become enabled as it may not know the Mode II/fixed TVBDs in the area and it cannot join the IBSS of another enabled Mode I TVBD before being enabled. Embodiments of these teachings are relevant to efficiently setting up and operating an IBSS. Though in the context of TVBDs and IBSSs, these teachings are not limited only to the IEEE 802.11af family of radio access technologies and are applicable for other types of ad hoc networking in the license-exempt band.
Relevant background may be seen at document IEEE P802.11af/D1.02: Wireless LAN Medium Access Control (MAC) and Physical layer (PHY) specifications; Amendment 3: TV White Spaces Operation (June 2011), as well as at the reference IEEE Draft P802.11-REVmb/D9.1: IEEE STANDARD FOR INFORMATION TECHNOLOGY—TELECOMMUNICATIONS AND INFORMATION EXCHANGE BETWEEN SYSTEMS—LOCAL AND METROPOLITAN AREA NETWORKS—SPECIFIC REQUIREMENTS PART 11: WIRELESS LAN MEDIUM ACCESS CONTROL (MAC) AND PHYSICAL LAYER (PHY) SPECIFICATIONS (July 2011).